Electricity and Control December 2023

ENERGY MANAGEMENT + THE INDUSTRIAL ENVIRONMENT

Figure 5: Induced voltage on dc string cables via tracker structure.

It is often seen as the outcome of the lightning risk analysis that a lightning protection system of LPL IV would be sufficient to protect the PV plant and keep damages below the tolerable value. In most cases this presents a risk, as the lightning risk analysis is conducted according to SANS 62305-2, which is aimed mainly at closed buildings and not free-field PV plants. Although the calculated outcome might indicate that LPL IV is sufficient, closer inspection may show it would be insufficient for a PV plant, if the differences of each PV plant are not taken into account. SANS 61643-32 makes explicit recommendation that LPSs for PV plants should be designed to a minimum of LPL III, due to the fact that lightning strikes commonly fall below 16 kA in such open areas. In experience and prac tical studies (obtaining information from the South African Weather Service), it has been noted for various different plants that anywhere between 45 and 70% of lightning strikes in a single storm have had peak values smaller than 16 kA, and could possibly not have been intercepted by an LPL IV lightning protection system. Thus, the system would not be sufficient in protecting the PV area, and damages would exceed the residual losses indicated in the results of a risk analysis. With the increase in demand for PV plants and in in stallation size, lightning risk also potentially increases. As the renewable energy industry is a cost-sensitive market, lightning protection is commonly overlooked, and this could result in high costs of damages and operational expenses. By addressing the three most common installation and de sign mistakes, it is possible to reduce the cost of lightning protection significantly and still maintain high levels of pro tection. It is strongly advised that these factors should al ways be considered when independent power producers, developers, installers, or owners of PV plants consult with a lightning protection engineering specialist. □

four levels (LPLs), each sized according to criteria for max imum and minimum peak values. We have seen how maxi mum values could overstress equipment, components and SPDs. It should also be noted that the minimum value of each LPL is important in the dimensioning and design of a lightning protection system (LPS). Lightning protection systems can be designed using three different methods, where the most comprehensive is known as the Rolling Sphere method. The method is based on electric field strength theory, dating back to the experi ments conducted by Benjamin Franklin using a kite. The goal is to determine possible strike locations for a downward lightning strike, using a 3D sphere representing the electric field strength around the tip of the downward leader. Any object with which the sphere makes contact in dicates a possible point where lightning could strike, that is, one offering a preferred lower-impedance path in compari son to air. For the most comprehensive lightning protection systems, focus is shifted to minimum lightning current val ues, to ensure smaller peak value current lightning strikes are also intercepted by designing with a smaller sphere, which would contact more objects. Figure 6 illustrates the concept.

For more information visit: www.dehn-africa.com

Figure 6: Concept of the 3D rolling sphere.

12 Electricity + Control DECEMBER 2023